In some diagnostic and therapeutic techniques, a catheter is inserted into a chamber of the heart and brought into contact with the inner heart wall. In such procedures, it is generally important that the distal tip of the catheter engages the endocardium with sufficient pressure to ensure good contact. Excessive pressure, however, may cause undesired damage to the heart tissue and even perforation of the heart wall.
For example, in intracardiac radio-frequency (RF) ablation, a catheter having an electrode at its distal tip is inserted through the patient's vascular system into a chamber of the heart. The electrode is brought into contact with a site (or sites) on the endocardium, and RF energy is applied through the catheter to the electrode in order to ablate the heart tissue at the site. Proper contact between the electrode and the endocardium during ablation is necessary in order to achieve the desired therapeutic effect without excessive damage to the tissue.
A number of patent publications describe catheters with integrated pressure sensors for sensing tissue contact. As one example, U.S. Patent Application Publication 2007/0100332, whose disclosure is incorporated herein by reference, describes systems and methods for assessing electrode-tissue contact for tissue ablation. An electro-mechanical sensor within the catheter shaft generates electrical signals corresponding to the amount of movement of the electrode within a distal portion of the catheter shaft. An output device receives the electrical signals for assessing a level of contact between the electrode and a tissue.
As another example, U.S. Pat. No. 6,695,808, whose disclosure is incorporated herein by reference, describes apparatus for treating a selected patient tissue or organ region. A probe has a contact surface that may be urged against the region, thereby creating contact pressure. A pressure transducer measures the contact pressure. This arrangement is said to meet the needs of procedures in which a medical instrument must be placed in firm but not excessive contact with an anatomical surface, by providing information to the user of the instrument that is indicative of the existence and magnitude of the contact force.
Other catheters with pressure sensors are described in U.S. Pat. No. 6,241,724 and U.S. Pat. No. 6,915,149, whose disclosures are incorporated herein by reference.
PCT International Publication WO 2007/067938, whose disclosure is incorporated herein by reference, describes a method for displaying catheter electrode-tissue contact in an electro-anatomic mapping and navigation system. The system provides an indication to the physician concerning the electrical coupling of an electrode, such as an ablative or mapping electrode, with a patient. The indication may be provided by changing the color or other display characteristics of the electrode on the navigation system display or by way of providing a waveform indicating the electrode coupling. This manner of providing electrode coupling information is said to minimize physician distraction.